Date Published: April 3, 2017
Publisher: Public Library of Science
Author(s): Shinya Kageyama, Toru Takeshita, Mikari Asakawa, Yukie Shibata, Kenji Takeuchi, Wataru Yamanaka, Yoshihisa Yamashita, Motohiro Komaki.
Increasing attention is being focused on evaluating the salivary microbiota as a promising method for monitoring oral health; however, its bacterial composition greatly differs from that of dental plaque microbiota, which is a dominant etiologic factor of oral diseases. This study evaluated the relative abundance of subgingival plaque-specific bacteria in the salivary microbiota and examined a relationship between the abundance and severity of periodontal condition in patients with periodontitis. Four samples (subgingival and supragingival plaques, saliva, and tongue coating) per each subject were collected from 14 patients with a broad range of severity of periodontitis before periodontal therapy. The bacterial composition was analyzed by 16S rRNA gene amplicon sequencing using Ion PGM. Of the 66 species-level operational taxonomic units (OTUs) representing the mean relative abundance of ≥ 1% in any of the four niches, 12 OTUs corresponding to known periodontal pathogens, including Porphyromonas gingivalis, were characteristically predominant in the subgingival plaque and constituted 37.3 ± 22.9% of the microbiota. The total relative abundance of these OTUs occupied only 1.6 ± 1.2% of the salivary microbiota, but significantly correlated with the percentage of diseased sites (periodontal pocket depth ≥ 4 mm; r = 0.78, P < 0.001), in addition to the abundance of subgingival plaque microbiota (r = 0.61, P = 0.02). After periodontal therapy, the total relative abundance of these 12 OTUs was evaluated as well as before periodontal therapy and reductions of the abundance through periodontal therapy were strongly correlated in saliva and subgingival plaque (r = 0.81, P < 0.001). Based on these results, salivary microbiota might be a promising target for the evaluation of subgingival plaque-derived bacteria representing the present condition of periodontal health.
The human oral cavity harbors numerous, diverse, indigenous microorganisms. They create distinct microbial communities on intraoral surfaces, such as the tooth surface, gingival crevice, tongue dorsum, and buccal mucosa, with different ecological conditions. Subgingival microbiota is comprised of a unique microbial community dominated by obligatory anaerobic and proteolytic bacteria, which are involved in the progression of periodontitis, one of the major causes of tooth loss. Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola are shown to be strongly associated with diseased periodontal pocket and are known as red complex, which has been the focus as the etiologic agents of periodontitis . Furthermore, based on the results of the open-ended 16S rRNA gene analyses, a recent systematic review added 17 bacterial taxa to the list of suspected periodontal pathobionts [2, 3].
Subgingival and supragingival plaques, saliva, and tongue coating samples (their microbiota were defined as SUBP, SUPP, SL, and TC, respectively) were collected twice from 14 patients with periodontitis who visited a dental clinic (5 women and 9 men; aged 35–73 years) at their initial visit (pre-therapy samples) and after periodontal therapy (approximately 2 years later; post-therapy samples). The subjects had completed periodontal therapy and received supportive therapy with maintenance care during the interval between the sample collections. Their clinical periodontal conditions improved from that during the initial sample collection (S1 Table).
This study identified 12 species-level OTUs that were characteristically more predominant in SUBP than in the other 3 microbiota (SUPP, SL and TC) and demonstrated that their relative abundances and shifts in relative abundance in SUBP and SL were strongly correlated with periodontal health. Our results showed that the composition of the SL was more similar to that of TC than that of SUBP, which is consistent to the findings of previous reports [10–13]. In addition, considering that these 12 OTUs made up 37.3 ± 22.9% of the SUBP, but accounted for only 1.6 ± 1.2% of the SL (Fig 2), bacteria derived from periodontal pockets are a minority assemblage of SL containing bacteria shed from various oral sites. Nevertheless, the present results showed that the relative abundance of the SUBP-specific OTUs in SL monitored by using a 16S rRNA gene deep sequencing approach can reflect that in SUBP, representing the condition of periodontal health.